Effects ofHymenaea courbaril leaf resin on the generalist herbivoreSpodoptera exigua (beet armyworm)

The hypothesis that leaf resin ofHymenaea courbaril (Leguminosae) functions as a defence against herbivory was tested in a series of experiments with the generalist herbivore, beet armyworm (Spodoptera exigua Hübn). Pure leaf resin obtained by steam distillation was incorporated into an artificial diet at 0.0%, 0.16%, 0.50%, and 1.60% (dry weight) in one experiment and 0.0%, 1.0%, and 3.2% (dry weight) in a second experiment;S. exigua larvae were reared on these diets. In four palatability experiments the amount of leaf area eaten was compared between pairs of different leaf material. Mortality due to viral infection of larvae in the first feeding experiment showed a dose-response to leaf resin concentration. In the second experiment larvae showed a dose-response in the reduction of pupal weight and delay of time to pupation. These are interpreted as a dose-related stress onS. exigua which occurs with increased resin concentration in the diet. In the palatability tests,S. exigua strongly preferred untreated to resintreated bean leaf disks, bean disks toH. courbaril immature leaf disks,H. courbaril immature leaf toH. courbaril mature leaf, and bean leaf disks toH. courbaril newly emerged leaf disks. From these results, we conclude thatH. courbaril leaf resins possess toxic and feeding-deterrent properties which make them effective as an herbivore defense.